1. Field of the Invention
The present invention relates to a device for controlling a liquid flow in a liquid channel. The present invention also relates to an assembly and integrated circuit in which this device is placed, and to a method for manufacture thereof.
2. Description of the Prior Art
Charged particles in a solution or suspension of liquid channel con be transported by applying an electric field substantially parallel to the liquid channel. Under the influence of the electric field positively and negatively charged particles will move in opposing directions. This transport is also referred to as electrophoresis.
Another mechanism for generating a liquid flow in a liquid channel is formed by so-called electro-osmosis. The liquid channel is in this case enclosed by an electric insulator. At the location of the transition between the insulator and the liquid are situated charged insulator particles which are chemically bound to the insulator. As a consequence of the charge of these insulator particles, particles with an opposing charge are formed close to the insulator wall in the liquid channel. The layer consisting of the chemically bound insulator particles and the liquid particles charged in opposing directions is also referred to as the electric double layer. As a result of the presence of these particles with opposing charge, which are not chemically bound to the insulator, and the above mentioned electric field applied parallel to the direction of the liquid channel, a liquid flow will be generated along the walls of the liquid channel. The liquid flow along the walls brings about a liquid flow across the entire diameter of the liquid channel as a result of the friction between the liquid particles.
The moving charged particles define a shear plane at some distance of the insulator wall. The electrical potential at the location of this shear plane is called the xcex6-potential (Zeta potential). The magnitude of the xcex6-potential depends inter alia on factors such as the type of liquid or insulator, the concentrations of the different particles in the liquid, the pH value and the like. The direction and the degree of liquid flow resulting from electro-osmosis can be controlled by changing these factors.
It can be deemed known to vary the potential of the outer surface of the insulator with a voltage source, as a result of which the above stated xcex6-potential in the liquid channel can be varied. Since the direction and speed of the liquid flow in the liquid channel depends on the magnitude of the xcex6-potential, the movement of the particles in the liquid can be controlled with the voltage source, i.e. the movement of particles resulting from electrophoresis can be enhanced or decreased. While there are indeed devices known which enable such a control of the liquid flow in a liquid channel, they have large dimensions and require very high control voltages in the order of magnitude of several kVs, so that in practice they cannot be integrated with standard electronic components such as transistors, integrated circuits and so on.
The object of the present invention is to obviate these drawbacks.
According to an aspect of the invention, a device is provided for this purpose for controlling a liquid flow in a liquid channel, comprising:
an elongate liquid holder in which a liquid channel is provided in longitudinal direction;
first voltage means for applying a first voltage difference over substantially the longitudinal direction of the liquid channel;
a conductor member arranged in at least a part of the liquid channel against the liquid holder;
an insulator member arranged in the liquid channel against at least the conductor member;
second voltage means for providing a second voltage difference between the conductor member and the liquid in the liquid channel; wherein the thickness of the insulator member is a maximum of 1 xcexcm and preferably in the order of magnitude of some tens of nanometres. In accordance with this aspect of the invention a device is therefore provided for controlling a liquid flow, wherein the functions of liquid container or liquid holder on the one hand and of insulator or xcex6-potential control layer on the other are separated, so that a great flexibility can be achieved in choice of material and method of manufacture.
According to a preferred embodiment of the invention the insulator member is formed from a thin layer or coating of insulator material, the conductor member and the liquid holder are combined and formed from a mechanically stable conductor material. The mechanically stable material provides in this case the required sturdiness of the device.
According to a further preferred embodiment of the invention the insulator member and the conductor member are formed from thin layers of respectively insulator material and conductor material, wherein the liquid holder is preferably formed from a mechanically stable material.
According to another aspect of the invention, a device is provided for controlling the liquid flow in a liquid channel, comprising:
an insulator member which defines an elongate liquid channel;
first voltage means for applying a first voltage difference over substantially the longitudinal direction of the liquid channel;
a conductor member arranged over at least a part of the outer surface of the insulator member;
second voltage means for providing a second voltage difference between the conductor member and the liquid in the liquid channel; wherein the distance between the outer surface and the inner surface of the insulator member is a maximum of 1 xcexcm and preferably in the order of magnitude of some tens of nanometres. By making the wall thickness of the insulator member so small, the control of the liquid flow can advantageously be performed with a small second voltage difference, for instance with a voltage difference of less than 20 Volt. At such small wall thicknesses there moreover occurs a reduced loss of power and an improved heat discharge is possible.
According to a further preferred embodiment of the invention the device can be directly connected to standard electronic elements or integrated circuits or can even be integrated therewith. This preferred embodiment can therefore be advantageously connected directly onto and controlled by the output of the standard electronic elements such as integrated circuits, without additional provisions being required therein.
According to a further preferred embodiment of the invention the insulator member and the conductor member are manufactured from optically transparent materials. This has the advantage that the content and/or composition of the content of the liquid channel can be optically detected in simple manner.
According to a further preferred embodiment of the invention the insulator member is constructed from two or more insulator part-members manufactured with materials of different xcex6-potential. This has the advantage that various flows with differing speeds and directions can be generated in the liquid channel without applying an external potential difference.
According to a further embodiment of the invention the insulator member is provided with two or more conductor members, to which mutually differing voltages can be applied. By applying different potentials to the conductor members, the associated xcex6-potentials in the liquid channel will accordingly differ from each other. This has the advantage that different flows with differing speeds and/or directions of movement can be generated within the same liquid channel.
According to another preferred embodiment the voltage means comprise two electrodes which are arranged in the liquid channel. Because the electrodes can be arranged in the liquid the distance between the electrodes can be reduced, at least relative to the distance in the case of external electrodes, to an order of magnitude of a few-micrometers. Lower voltages are hereby sufficient to obtain the desired field strength of the electric field.
According to a further aspect of the invention, a system is provided for analysis and/or synthesis of chemical solutions or suspensions, wherein one or more of the above stated devices is used. According to a preferred embodiment of this system, this system comprises control means for controlling one or more liquids through a network of said devices.
According to a further preferred embodiment the network of said devices comprises one or more feed channels, two intermediate channels branched from the feed channels and one or more drain channels connected to the intermediate channels, wherein the intermediate channels are provided with gates which are supplied with voltage such that in the intermediate channels a substantially loop-like liquid flow results. Using such loop-like liquid flows the liquid in the intermediate channels can be circulated so that the liquid is mixed or enters into a chemical reaction.
According to a further aspect of the present invention, a pump system is provided for circulating liquid, in which preferably one or more of the above stated devices are used, comprising:
a liquid holder in which are provided a liquid feed channel and a liquid drain channel branched from the liquid feed channel;
first voltage means for applying an electric field in the longitudinal direction of the liquid feed channel;
a first and a second gate electrode which are placed on either side of the connection of the liquid drain channel to the liquid feed channel;
second voltage means for providing the first and second gate electrode with voltage;
control means for adjusting the first and second voltage means such that a pressure build-up occurs at the location of said connection and the liquid is drained via the liquid drain channel.
With the above stated system a pump can be realized on micro-scale, wherein the drain channel of the pump is voltage-free, this being advantageous since the drain channel can thereby be connected more easily to peripheral equipment and the like.
According to further embodiments of thee above stated pump system, the first voltage means generate an electric field alternately in a first and in a second, opposing direction in the liquid feed channel and the second voltage means, substantially synchronously with the first voltage means, switch the first gate electrode into enhancement mode and the second gate electrode into a reversement mode and vice versa. By circulating the liquid in such a manner polarization effects, such as the creation of air bubbles as a result of electrolysis, do not occur, which polarization effects could have an adverse effect on the operation of the pump.
According to a further aspect of the present invention, an electronic circuit is provided into which the above stated device is integrated.
According to a further aspect of the invention a method is provided for manufacturing the above stated device, comprising of:
etching a channel in a wafer;
depositing insulating material on the wafer;
manufacturing a glass plate;
anodic binding of the wafer on the glass plate;
etching the wafer; and
fixing the conductor member.
By manufacturing the device in this manner liquid channels with the correct properties and very small wall thicknesses of a few tens of nanometres can be realized.
According to a further aspect of the present invention a method is provided for mixing two or more liquids, comprising of:
supplying the liquids via one or more liquid channels;
mixing the liquids by circulating the supplied liquid, preferably in the above stated system;
draining the liquids via one or more liquid drain channels.